A ceramic electrostatic chuck is fabricated by sandwiching an electrode between ceramic dielectric substrates made of e.g. alumina, followed by firing. An electrostatic clamping force is applied to the incorporated electrode. Thus, the electrostatic chuck clamps a substrate such as a silicon wafer by electrostatic force. In such an electrostatic chuck, an inert gas such as helium (He) is passed between the front surface of the ceramic dielectric substrate and the back surface of the clamped target substrate to control the temperature of the clamped target substrate.
For instance, the temperature increase of the substrate may be associated with processing in an apparatus for processing a substrate such as a CVD (chemical vapor deposition) apparatus, sputtering apparatus, ion implantation apparatus, and etching apparatus. In the electrostatic chuck used in such an apparatus, an inert gas such as He is passed between the ceramic dielectric substrate and the clamped target substrate to bring the substrate into contact with the inert gas. Thus, the temperature increase of the substrate is suppressed.
In the electrostatic chuck for controlling the substrate temperature with an inert gas such as He, a hole (gas feed channel) for feeding an inert gas such as He is provided in the ceramic dielectric substrate and a base plate for supporting the ceramic dielectric substrate.
Here, electric discharge may occur in the gas feed channel when the substrate is processed in the apparatus. Patent Literature 1 discloses an electrostatic chuck in which the insulation performance in the gas feed channel is improved by providing a ceramic sintered porous body in the gas feed channel. The structure and the film hole of the ceramic sintered porous body are used as a gas flow channel. Patent Literature 2 discloses an electrostatic chuck in which a discharge prevention member of the processing gas flow channel made of a ceramic porous body and intended for preventing discharge is provided in the gap for gas diffusion. Patent Literature 3 discloses an electrostatic chuck in which arc discharge is reduced by providing a dielectric insert made of a porous dielectric such as alumina.
However, a sufficient insulation breakdown voltage cannot be achieved simply by providing a ceramic porous body in the gas feed channel. Further enhancement of insulation breakdown voltage is needed to provide an electrostatic chuck supporting various conditions in the processing apparatus.
Furthermore, the porous body has high porosity. Thus, the heat transfer coefficient from the ceramic porous body to the ceramic dielectric substrate is lower than the heat transfer coefficient from the metallic base plate to the ceramic dielectric substrate. Thus, the temperature difference is likely to increase between the temperature of the substrate cooled by a conduction gas passed from the gas feed channel and the temperature of the substrate with no conduction gas passed. That is, regions with a large within-wafer temperature difference (what is called hot spots and cold spots) occur near the ceramic porous body throughout the substrate. This causes the problem of failing to perform temperature control with high wafer temperature uniformity.